1. Field of the Invention
The present invention is directed to distillation. It has particular, but not exclusive, application to systems that purify water by distillation.
2. Background Information
One of the most effective techniques for purifying water is to distill it. In distillation, the water to be purified is heated to the point at which it evaporates, and the resultant vapor is then condensed. Since the vapor leaves almost all impurities behind in the input, feed water, the condensate that results is typically of a purity much higher in most respects than the output of most competing purification technologies.
But the amount of heat energy that needs to be imparted to produce an acceptable rate of evaporation is high, so distillation is expensive if most of the energy is not recovered. For this reason, distillers that employ the invention to be described below employ heat exchangers such as counterflow heat exchangers to recover heat from the distillation operation's condensate and/or concentrate output. They do so by conducting that heat to incoming feed liquid, which needs to be heated for distillation.
Such energy recovery is crucial if any efficiency is to be achieved. But condensate purity can be compromised if defects occur in, say, a counterflow heat exchanger's divider element that conducts heat between the feed liquid and the condensate but ordinarily prevents fluid communication between the passages in which those two fluids flow. Age, corrosion, or other factors, for example, may cause the divider to develop a hole small enough to go unnoticed but large enough to permit some of the untreated feed liquid to mix with the previously purified condensate.